docs: def _load_knownGene(filename):
          """ Load UCSC knownGene table.
  
          Parameters
          ----------
          filename : str
              path to knownGene file
  
          Returns
          -------
          df : pandas.DataFrame
              knownGene table if loading was successful, else None
          """
          try:
              df = pd.read_table(
                  filename,
                  names=[
                      "name",
                      "chrom",
                      "strand",
                      "txStart",
                      "txEnd",
                      "cdsStart",
                      "cdsEnd",
                      "exonCount",
                      "exonStarts",
                      "exonEnds",
                      "proteinID",
                      "alignID",
                  ],
                  index_col=0,
              )
              df["chrom"] = df["chrom"].str[3:]
              return df
          except Exception as err:
              print(err)
              return None